Global Namespace for a Hierarchical Set of File Systems

1. A method for storage management in a hierarchical set of file systems, the method comprising: creating a structure for the hierarchical set of file systems including a top-file system and sub-file systems that each include files and directories; tracking directories for sub-file systems of the hierarchical set of file systems; receiving a request to create an additional directory; creating, based on applying a directory creation policy, the additional directory in a sub-file system of the hierarchical set of file systems while providing that each directory resides in only one sub-file system; and upon a request by a particular sub-file system for more inodes without any inodes available, revoking inode numbers from at least one other sub-file system having unused inodes; wherein failure in one sub-file system has no affect on other sub-file systems in the hierarchical set of file systems, and each directory in the sub-file systems is named using an inode number of a directory.

2. The method of claim 1 , wherein: applying the directory creation policy comprises: selecting a sub-file system with the largest available space upon determining that the additional directory is a parent directory in the top-file system; and a namespace in the top file system and pointers to each of the multiple sub-file systems include a name of a directory in a sub-file system that is its inode number in the top file system portion.

3. The method of claim 1 , wherein applying the directory creation policy comprises: selecting a sub-file system having available space at least as large as an estimated size requirement for the additional directory upon determining that the additional directory is a parent directory in the top-file system.

4. The method of claim 1 , wherein applying the directory creation policy comprises: selecting, in a round-robin fashion, a sub-file system having available space for the additional directory upon determining that the additional directory is a parent directory in the top-file system.

5. The method of claim 1 , wherein applying the directory creation policy comprises: selecting a sub-file system containing a parent directory of the child directory upon determining that the additional directory is a child directory.

6. The method of claim 1 , wherein tracking comprises: for each directory in a sub-file system: maintaining a corresponding directory in a top-file system; and maintaining a symbolic pointer in the corresponding directory which points from the corresponding directory to the sub-file system where the tracked directory resides.

7. The method of claim 5 , further comprising: creating a corresponding directory in the top-file system; creating a symbolic pointer in the corresponding directory in the top-file system which points from the corresponding directory to the particular sub-file system containing the additional directory; and parallelizing file system operations by issuing the file system operations on any number of sub-file systems simultaneously.

8. The method of claim 7 , wherein directories are stored at a root for the sub-file systems.

9. A computer program product for storage management in a hierarchical set of file systems, the computer program product comprising a computer readable storage medium having program instructions embodied therewith, the program instructions executable by a processor to cause the processor to: create, by the processor, a structure for the hierarchical set of file systems including a top-file system and sub-file systems that each include files and directories; track, by the processor, directories for sub-file systems of the hierarchical set of file systems; receive, by the processor, a request to create an additional directory; create, based on applying a directory creation policy by the processor, the additional directory in a sub-file system of the hierarchical set of file systems while providing that each directory resides in only one sub-file system; and upon a request by a particular sub-file system for more inodes without any inodes available, revoke, by the processor, inode numbers from at least one other sub-file system having unused inodes; wherein failure in one sub-file system has no affect on other sub-file systems in the hierarchical set of file systems, and each directory in the sub-file systems is named using an inode number of a directory.

10. The computer program product of claim 9 , wherein: applying the directory creation policy further comprising program instructions executable by the processor to cause the processor to: select, by the processor, a sub-file system with the largest available space upon determining that the additional directory is a parent directory in the top-file system; and a namespace in the top file system and pointers to each of the multiple sub-file systems include a name of a directory in a sub-file system that is its inode number in the top file system portion.

11. The computer program product of claim 9 , wherein applying the directory creation policy further comprising program instructions executable by the processor to cause the processor to: select, by the processor, a sub-file system having available space at least as large as an estimated size requirement for the additional directory upon determining that the additional directory is a parent directory in the top-file system.

12. The computer program product of claim 9 , wherein applying the directory creation policy further comprising program instructions executable by the processor to cause the processor to: select, by the processor, in a round-robin fashion, a sub-file system having available space for the additional directory upon determining that the additional directory is a parent directory in the top-file system.

13. The computer program product of claim 9 , wherein applying the directory creation policy further comprising program instructions executable by the processor to cause the processor to: select, by the processor, a sub-file system containing a parent directory of the child directory upon determining that the additional directory is a child directory.

14. The computer program product of claim 13 , further comprising program instructions executable by the processor to cause the processor to: create, by the processor, a corresponding directory in the top-file system; create, by the processor, a symbolic pointer in the corresponding directory in the top-file system which points from the corresponding directory to the particular sub-file system containing the additional directory; and parallelize, by the processor, file system operations by issuing the file system operations on any number of sub-file systems simultaneously.

15. The computer program product of claim 13 , further comprising program instructions executable by the processor to cause the processor to: maintain, by the processor, a corresponding directory in a top-file system; and maintain, by the processor, a symbolic pointer in the corresponding directory which points from the corresponding directory to the sub-file system where the tracked directory resides.

16. The computer program product of claim 15 , wherein directories are stored at a root for the sub-file systems.

17. An apparatus comprising: a memory storing instructions; and one or more processors executing the instructions to: create a structure for a hierarchical set of file systems including a top-file system and sub-file systems that each include files and directories; track directories for sub-file systems of the hierarchical set of file systems; receive a request to create an additional directory; create, based on applying a directory creation policy, the additional directory in a sub-file system of the hierarchical set of file systems while providing that each directory resides in only one sub-file system; and upon a request by a particular sub-file system for more inodes without any inodes available, revoke inode numbers from at least one other sub-file system having unused inodes; wherein failure in one sub-file system has no affect on other sub-file systems in the hierarchical set of file systems, and each directory in the sub-file systems is named using an inode number of a directory.

18. The apparatus of claim 17 , wherein the one or more processors further execute instructions to: create a corresponding directory in the top-file system; create a symbolic pointer in the corresponding directory in the top-file system which points from the corresponding directory to the particular sub-file system containing the additional directory; and parallelize file system operations by issuing the file system operations on any number of sub-file systems simultaneously; wherein applying the directory creation policy comprises: selecting a sub-file system containing a parent directory of the child directory upon determining that the additional directory is a child directory.

19. The apparatus of claim 18 , wherein directories are stored at a root for the sub-file systems, and a namespace in the top file system and pointers to each of the multiple sub-file systems include a name of a directory in a sub-file system that is its inode number in the top file system portion.